Generally, a hybrid vehicle includes a high voltage main battery which is a fuel cell and a low voltage auxiliary battery for supplying a voltage to each electric load of the vehicle. In addition, a low voltage DC-DC converter (LDC) for reducing a voltage output from the main battery is provided between the main battery and the auxiliary battery.
FIG. 1 shows a circuit configuration of a conventional low voltage DC-DC converter. Referring to FIG. 1, in the circuit of the conventional low voltage DC-DC converter, a maximum voltage of a main switch is inversely proportional to a capacitance of a capacitor. More specifically, as the capacitance of the capacitor increases, the maximum voltage of the main switch decreases, and as the capacitance of the capacitor decreases, the maximum voltage of the main switch increases. That is, as the capacitance of the capacitor is increased, the maximum voltage of the main switch is reduced, such that the main switch can be more freely selected.
On the other hand, in the circuit of the conventional low voltage DC-DC converter, as the capacitance of the capacitor is reduced, a resonance frequency of the capacitance and inductance is located outside a frequency band for stably controlling the low voltage DC-DC converter, resulting in making the controllability easy. However, if the capacitance of the capacitor is increased to reduce the maximum voltage of the main switch, the resonance frequency of the capacitance and the inductance may be located within the frequency band for stable control of the low voltage DC-DC converter, which leads to the deterioration in the controllability.